Start by clarifying requirements and scale, then explain the hash ring with virtual nodes and weighted mapping. Walk through the API design and demonstrate how virtual nodes minimize remapping, and finally discuss trade-offs and edge cases.
Pro tip: Quantify the improvement: with V virtual nodes per physical node, adding/removing a node remaps only ~1/(N+1) of keys, and weights can be implemented by allocating virtual nodes proportionally. Mention that consistent hashing is used in production systems like Dynamo and Cassandra to show practical awareness.
Ask about expected number of nodes, keys, read/write patterns, and consistency needs. Confirm that the system should minimize key remapping when nodes are added or removed.
Explain mapping both nodes and keys to a circular hash space (e.g., 0 to 2^32-1). Introduce virtual nodes: each physical node is represented by multiple points on the ring to improve balance and enable weighting.
Specify addNode(nodeId, weight), removeNode(nodeId), and getNode(key). Describe using a sorted structure (e.g., balanced BST or sorted array) for efficient lookup, and a map to track virtual nodes per physical node.
For getNode(key), hash the key and find the first virtual node clockwise on the ring. Show that adding/removing a node only affects keys in the adjacent arc, and with V virtual nodes, remapping is ~1/(N+1) of keys.
Cover choice of V (balance vs. memory), handling node failures, replication, and potential hotspots. Mention alternatives like rendezvous hashing and when they might be preferable.
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